Positioning system is used to determine position information. The positioning system may be a Global Positioning Satellites (GPS) system and may be provided by the United States Department of Defense (DOD) and other satellite tracking systems to help determine the position information. GPS may also be provided by Russia or countries in Europe. GPS is based on a number of orbiting satellites that broadcast signals to a number of GPS receivers. The signals broadcast from the satellites may include the identity and position of the satellite that broadcasts the signals. In addition, the signals may include time when the signals were broadcast. There may be other positioning systems that can augment GPS to provide better position inside buildings.
A GPS receiver may use this information to calculate its position (latitude and longitude), altitude, velocity, heading and precise time of day using signals received from at least four GPS satellites. Each GPS satellite may broadcast or transmit two signals, an L1 signal and an L2 signal. The L1 signal may be modulated with two pseudo-random noise codes, the protected code and the course/acquisition (C/A) code. Each GPS satellite may have its own unique pseudo-random noise code. Civilian navigation GPS receivers may only use the C/A code on the L1 frequency.
FIG. 1 illustrates one example of a prior art positioning system. Positioning system 100 may be a GPS and may include a GPS receiver 110 and four GPS transmitters or satellites 120A, 120B, 120C and 120D. There may be multiple GPS receivers and multiple GPS transmitters. The GPS receiver 110 may receive information from the GPS transmitters 120A, 120B, 120C and 120D, and uses the information to determine its position with respect to GPS the transmitters 120A, 120B, 120C and 120D. The GPS receiver 110 may measure the time required for the broadcast signal to travel from the GPS transmitters 120A–120D to the GPS receiver 110. This may include the GPS receiver 110 generating its own pseudo-random noise code identical to each GPS transmitter's code and precisely synchronizing the two codes to determine how long the GPS transmitter's code takes to reach the GPS receiver 110. By performing the process with at least four GPS transmitters 120A–120D, error in the calculation of position and time may be reduced. As the GPS receiver 110 moves around, the position of the GPS receiver 110 may be re-calculated.